The present invention is directed in general to determining the direction of locomotive travel during dynamic braking from current flow in the traction motors, and more specifically to an apparatus that uses the current flow information to update the direction of travel information stored within the locomotive control system, where one function of the locomotive control system is to prevent traction motor plugging when motoring is requested in the direction opposite to the last known direction of locomotive travel.
The DC (direct current) diesel-electric locomotive control system allows operator control of the traction motors, which provide the propulsion forces for the locomotive. These controller mechanisms typically include a throttle control handle for controlling the speed/horsepower of the locomotive or for activating the dynamic brakes, and a direction control handle (also referred to as a reverser handle) for controlling the direction of the applied propulsion forces. The throttle control handle has a series of notches (generally eight such notches) with higher numbered notches indicating the application of higher propulsive forces to increase the speed and/or horsepower of the locomotive. The lowest notch on the throttle handle is referred to as the xe2x80x9cidlexe2x80x9d position. In this position, no propulsion forces are applied by the traction motors. A request for xe2x80x9cmotoringxe2x80x9d by the locomotive operator requires movement of the throttle handle to one of the notch positions while the direction control handle is in the forward or reverse position, as desired, at which time tractive forces, in proportion to the requested notch number, are applied to the locomotive wheels.
One deleterious effect of operator error is traction motor plugging. As is known in the art, generally, motor plugging occurs when a motoring call is made while the locomotive wheels are moving in a direction opposite to the direction of the motoring call, which is determined by the position of the direction handle. That is, if the locomotive is coasting backwards and the reverser handle is in the forward position when a motoring call is made, the motors will plug. Similarly, if the locomotive is coasting forward and the direction handle is in the reverse position when a motoring call is made, the motors will plug. The plugging action subjects the motors to traumatic forces and currents that can cause considerable damage and possibly destruction of the motors.
The locomotive control system is designed to obviate traction motor plugging under certain circumstances. For instance, assume the locomotive is moving in the forward direction under the influence of propulsion forces provided by the traction motors (that is, xe2x80x9cmotoringxe2x80x9d). Movement of the throttle handle to the idle position discontinues the motoring call but the locomotive continues to coast forward. At this point, the locomotive control system, one feature of which is designed to obviate traction motor plugging, xe2x80x9cremembersxe2x80x9d the last direction handle position when motoring was called for (i.e., the forward position) and assumes this is the current direction of locomotive travel. The control system will not allow a motoring call in the reverse direction, because the reverse direction is opposite to the assumed or remembered forward direction of locomotive travel. In this way, the opportunity for traction motor plugging is precluded. But the control system will permit a forward motoring call because the call direction is the same as the remembered direction. To override the control system and allow a reverse call, the train must slow down to a very slow speed (e.g., in one embodiment one mile per hour) or stop before the control system lock-out mechanism is disabled. At these very slow speeds, although traction motor plugging does occur, the effects are of lesser consequence. It should be noted that the direction handle can always be physically moved; there is no mechanical lockout applied to the reverser handle. The lockout is effectuated through the controller software.
Obviously, it is an important responsibility of the locomotive operator to prevent traction motor plugging by a constant awareness of the direction of travel as compared with the direction handle position. However, various locomotive controls have been developed, including those of the prior art as discussed above and those of the present invention, as a means of protecting against operator error and consequent motor plugging.
Braking of trains, and in particular diesel-electric locomotives, is accomplished by air brakes on the locomotive and cars and by dynamic brakes. Both of these braking actions are well known in the art. In dynamic braking, the motors, driven by the moving wheels of the locomotive, act as generators and the current generated is dissipated by a bank of resistors. The resistors convert the current into heat, which in turn is dissipated by a fan-driven cooling system.
Certain of the above mentioned difficulties associated with the plugging of locomotive traction motors can be overcome by the present invention, which relates to a novel and unobvious approach for determining the direction of locomotive travel while in dynamic braking mode. This direction information is sent to the locomotive control system for updating the travel direction information stored there, so as to prohibit a motoring call for movement in the opposite direction.